This study is concerned with a numerical investigation of the mixing flow in multilobe mixers. Predictions are obtained using a finite-volume method which incorporates a second-order difference scheme. The irregular boundaries are fitted by curvilinear nonorthogonal grids and the grid points are arranged in the collocated manner. A method is described to generate suitable three-dimensional grids to cover both the lobe region and the mixing duct. Computations are undertaken to examine the effects of lobe geometry on the mixing performance. Results indicated that the convex lobe contour can lead to stronger vortex flow and, thus, better mixing because of its large slope. As for the geometry of the lobe trailing edge, a sinusoidal shape with wide peak region gives rise to well-organized vortices and the mixing performance is enhanced. Also revealed is the mechanism which, resulting in efficient mixing in the mixer, is clearly identified.